1. Field of the Invention
The present invention relates to a vibration motor, more particularly relates to a vibration motor of a structure suitable for mounting on a printed circuit board etc.
2. Description of the Related Art
In the past, as a vibration motor of a structure suitable for surface mounting on a printed circuit board, as disclosed in Japanese Patent Publication (A) No. 11-234943, there has been known one having a motor body with an eccentric weight attached to a motor shaft, a metal holder frame provided with a motor holding part for fitting inside it and holding that motor case, and a pair of external connection terminal pieces (motor terminals) attached to a plastic end cap for closing an opening of the motor case at the side opposite to the eccentric weight, wherein the flat back surfaces of the metal holder frame and a pair of external connection terminal pieces are surface mounted by bringing them into contact, through coating cream solder, with bonding patterns and power feed patterns formed on the printed circuit board and by reflow soldering.
The many electrical components mounted on printed circuit boards in mobile phones and other thin devices are being made increasing thinner and smaller. Vibration motors, however, have rotating eccentric weights. In order to secure a predetermined vibration force, it is physically impossible to shorten the distance from the center of rotation to the outermost point of the eccentric weight. The specific gravity of the tungsten or other heavy metal forming the eccentric weight is also limited. Rather, to obtain a stronger vibration force than the present, the eccentric weights are expected to become larger. As opposed to this, if trying to reduce the area occupied on the board, since the motor body is set on the board surface in a horizontal prone posture, even if increasing the axial length or increasing the girth, assuming the same motor performance, the effect of reduction of the occupied area is not improved that much. There is an increasingly stronger trend toward a tradeoff between the increased size of the eccentric weight and the smaller size of the motor body.